English

Projective Ore-Degree Conditions for Intersection Theorems in Vector Spaces

Combinatorics 2026-07-28 v1

Abstract

Let VV be an nn-dimensional vector space over the finite field Fq\mathbb F_q, and let F[Vk]\mathcal F\subsetneq\genfrac{[}{]}{0pt}{}{V}{k}. The \emph{projective Ore-degree} of F\mathcal F is the minimum, over all kk-subspaces SFS\notin\mathcal F, of the sum of the F\mathcal F-degrees of the projective points contained in SS. We prove sharp projective Ore analogues of the vector-space Erd\H{o}s--Ko--Rado and Hilton--Milner theorems. The Ore--Erd\H{o}s--Ko--Rado theorem holds for n2k+1n\ge2k+1, with equality only for a full point-star. For nontrivial intersecting families, we determine the sharp Ore--Hilton--Milner threshold, together with the complete equality classification, when q3q\ge3 and n2k+1n\ge2k+1, or when q2q\ge2 and n2k+2n\ge2k+2. We further determine a sharp projective Ore-degree threshold forcing a direct-sum matching of size ss when s3s\ge3 and n(2s1)ks+4n\ge(2s-1)k-s+4, and derive a multicolour Ramsey consequence.

Cite

@article{arxiv.2607.25598,
  title  = {Projective Ore-Degree Conditions for Intersection Theorems in Vector Spaces},
  author = {Mengyu Cao and Mei Lu and Xuyang Yan and Haixiang Zhang},
  journal= {arXiv preprint arXiv:2607.25598},
  year   = {2026}
}